1. Field of the Invention
The present invention relates generally to an optical information processing device and an optical information recording/reproducing device in each of which a coherent light source is adapted, and particularly to a high-density optical disk recording/reproducing device that has a crosstalk removing function for removing a crosstalk component coming from adjacent tracks, and obtains a super-resolution condensed light spot in a size smaller than a diffraction limit.
2. Related Background Art
Recently, digital versatile disks (hereinafter abbreviated as DVDs) have been put to practical use, and this has led to a drastic increase in a storage capacity of an optical disk, allowing high-quality long-time motion picture information to be recorded therein. On the other hand, the high-definition motion picture broadcasting typified by HDTV broadcasting also is about to come into practical use, and this further accelerates the research and development of mass storage devices. Besides, optical disks such as compact disks (hereinafter abbreviated as CDs) and DVDs are widely utilized for external storage for computers, and as the performance of a computer is enhanced rapidly, higher-densification of an optical disk is earnestly demanded in the information processing and information communication fields. Particularly, as computers came to have improved performance, digital video cameras and digital still cameras started to be widely used, and then occasions for dealing massive acoustic imaging data increased. Consequently this caused high-speed-accessible large-capacity rewritable optical disks to occupy a more significant position than ever.
The expansion of the capacity of an optical disk is achieved by recording smaller marks in an optical disk or by reproducing information from a smaller pit, and the mark size or the pit size is limited by a size of a light spot that is determined by a light source wavelength of an optical pickup for reading information and a numerical aperture of an objective lens. If the size of a pit on a track provided in a spiral form, the size being in the line direction, is reduced to be equal to or smaller than the limit, a sufficient signal amplitude cannot be obtained. If a space between adjacent tracks is narrowed to be equal to or smaller than the limit, a drawback occurs in that marks in adjacent tracks are erased during a recording operation, and a drawback of crosstalk occurs in that signals from adjacent tracks interfere with reproduced signals during a reproducing operation, thereby hindering accurate signal recording/reproduction.
A super-resolution technique has been proposed as a technique to enable high densification beyond the limit of the light spot size. For instance, with a conventional optical pickup shown in FIG. 13A, a light spot 30′ in a size smaller than the diffraction limit is obtained utilizing a phase filter 3′ having circular zones (see FIG. 13C).
Though a spot width of a mainlobe is decreased as compared with a normal light spot, however, the light spot 30′ has an increased sidelobe outside the mainlobe, as shown in FIG. 13B. Therefore, when a conventional optical pickup as shown in FIG. 13A is used for reproduction, the sidelobe irradiates pits before and after the pit irradiated by the mainlobe, and tracks adjacent to the track irradiated by the mainlobe. As a result, reflection light of the sidelobe is mixed with reflection light of the mainlobe and is detected by a light detector 7′. This causes noise signals to increase, thereby causing the signal quality to degrade.